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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Practical point-to-point free-space quantum key distribution over .5 km

W. T. Buttler, Richard Hughes, Paul G. Kwiat, S. K. Lamoreaux, George L. Morgan, J. E. Nordholt, Charles G. Peterson

Published Jul 19, 1999• 0 citations
Publisher

Abstract

We have demonstrated point-to-point single-photon quantum key distribution over a free-space optical path of approximately 475 m under daylight conditions. This represents an increase of > 1,000 times farther than any reported point-to-point demonstration, and > 6 times farther than the previous folded path daylight demonstration. We expect to extend the daylight range to 2 km or more within the next few months. A brief description of the system is given here.

DOI
10.1117/12.354778

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We have demonstrated point-to-point single-photon quantum key distribution over a free-space optical path of approximately 475 m under daylight conditions. This represents an increase of > 1,000 times farther than any reported point-to-point demonstration, and > 6 times farther than the previous folded path daylight demonstration. We expect to extend the daylight range to 2 km or more within the next few months. A brief description of the system is given here.
Quantum cryptography is an emerging technology in which two parties may simultaneously generate shared, secret cryptographic key material using the transmission of quantum states of light. The security of these transmissions is based on the inviolability of the laws of quantum mechanics and information-theoretically secure post-processing methods. An adversary can neither successfully tap the quantum transmissions, nor evade detection, owing to Heisenberg's uncertainty principle. In this paper we describe the theory of quantum cryptography, and the most recent results from our experimental free-space system with which we have demonstrated for the first time the feasibility of quantum key generation over a point-to-point outdoor atmospheric path in daylight. We achieved a transmission distance of 0.5 km, which was limited only by the length of the test range. Our results provide strong evidence that cryptographic key material could be generated on demand between a ground station and a satellite (or between two satellites), allowing a satellite to be securely re-keyed in orbit. We present a feasibility analysis of surface-to-satellite quantum key generation.
We have demonstrated quantum key distribution (QKD) (Bennett C H and Brassard G 1984 Proc. IEEE Int. Conf. on Computers, Systems, and Signal Processing (Bangalore, India) p 175) over a 10 km, 1-airmass atmospheric range during daylight and at night. Secret random bit sequences of the quality required for the cryptographic keys used to initialize secure communications devices were transferred at practical rates with realistic security. By identifying the physical parameters that determine the system's secrecy efficiency, we infer that free-space QKD will be practical over much longer ranges under these and other atmospheric and instrumental conditions.
Quantum cryptography is an emerging technology in which two parties may simultaneously generate shared, secret cryptographic key material using the transmission of quantum states of light. The security of these transmissions is based on the inviolability of the laws of quantum mechanics and information-theoretically secure post-processing methods. An adversary can neither successfully tap the quantum transmissions, nor evade detection, owing to Heisenberg's uncertainty principle. In this paper we describe the theory of quantum cryptography, and the most recent results from our experimental free-space system with which we have demonstrated for the first time the feasibility of quantum key generation over a point-to-point outdoor atmospheric path in daylight. We achieved a transmission distance of 0.5 km, which was limited only by the length of the test range. Our results provide strong evidence that cryptographic key material could be generated on demand between a ground station and a satellite (or between two satellites), allowing a satellite to be securely re-keyed in orbit. We present a feasibility analysis of surface-to-satellite quantum key generation.